为什么Python使用py在Windows上运行程序

我有一个像这样运行的python脚本:

python3 script.py

This works fine on Linux and Mac. However it doesn't on Windows. Comments I've read, and the official Windows FAQ recommend using this instead on Windows:

py -3 script.py

But the FAQ doesn't explain why. Why does Windows have a unique execution method, and why is it only for Windows?

我真的需要诉诸这种丑陋的黑客手段吗?

if (windows)
   run("py -3 script.py")
else
   run("python3 script.py")